First of all, congrats on the launch of in-app Messaging 👏 It must have been a huge project for you.
The first use case I thought for this feature isn't covered yet (and I'm surprised it hasn't been asked for already) → the ability to create a group conversation with the participants of a club event!
(similar to what Google Chat does for your meetings)
We have a club of around 50 active members which mostly revolves around a WhatsApp group. We create weekly club rides on Strava and share them on WhatsApp. There's between 5 to 20 participants for each ride.
Usually when someone is late or lost the group, he has to message everyone on WhatsApp instead of just messaging the persons present on the ride.
It would be great to have group conversations directly created for each club event. If the conversation was not used the day after the event, it disappears automatically. It would incentivize sharing pictures from that ride, maybe some trash-talking pre-event, etc